This invention relates to toluene sulfonic acid derivatives having improved physical properties. More particularly this invention relates to 2-chloro-5-amino-para-toluene sulfonic acid, 4-amino-meta-toluene sulfonic acid, and 6-chloro-4-amino-meta-toluene sulfonic acid having improved physical properties. This invention also relates to an improved method for obtaining said toluene sulfonic acid derivatives from aqueous solutions of their respective salts.
In one commercial process for making said toluene sulfonic acid derivatives, the desired compound is precipitated in a batch-wise manner from an aqueous salt solution of such compound by adding slightly more than the stoichiometric amount of a mineral acid in one charge to the total batch of salt solution and allowing the pH of the mixture to decrease as the reaction proceeds. The precipitate is usually removed by filtration in the form of a wet presscake which, due to its low bulk density and the affinity of the product for water, requires long lengths of time to be dried.
The dried product which results from the foregoing process has many undesirable physical properties. Such a product is, for example, extremely difficult to handle due to its dusting characteristics and is also difficult to use in further synthesis procedures due to its resistance to wetting. Such a resistance to wetting makes the formation of solutions containing such a product very difficult, even with the use of wetting agent. It is also impractical to use the wet presscake which is formed by the foregoing procedure directly in the synthesis of pigmentary compositions due in part to the large amounts of water retained therein and the non-uniformity of the presscake which makes a reliable assay impossible.